This invention relates to a package of sheets for use in thermal recording (hereunder also referred to as "thermal sheets" or "thermal films"), as well as a supply magazine of sheetings such as thermal films the sensitivity of which varies with humidity. More particularly, the invention relates to a package and a magazine of thermal recording sheets that are adapted to have a moisture resisting structure.
The thermal printer is a thermal image recording apparatus that performs image recording by thermal transfer. With this apparatus, a thermal head having a multiple of heat generating elements is pressed onto a thermal film such that the heat generating elements are selectively actuated to generate heat in accordance with applied image signals, whereby imagewise development occurs on the thermal film to produce a recorded image.
Stated m ore specifically, a roll of thermal films in the apparatus unwound and transported by a mechanism comprising a belt conveyor, nip rollers and so forth to be carried to the image recording zone, where the film is transported mechanically in one direction for auxiliary-scanning while, at the same time, the heat generating elements in the thermal head that are arranged in a direction perpendicular to the transport of the film are selectively actuated to generate heat in an imagewise pattern to perform main scanning, whereby a thermally transferred image is developed on the film. After this procedure of image recording, the film is cut into sheets, transported and ejected onto the tray.
Also known in the art are a digital radiographic system using a stimulable phosphor sheet, as well as CT (computer tomography), MR (magnetic resonance imaging) and other medical image recording apparatus. Conventionally, these apparatus have been operated by a "wet system", in which silver salt photographic materials carrying taken pictures or recorded images are subjected to wet processing to yield reproduced images. As an alternative method, a "dry system" has recently drawn increasing attention and an apparatus using thermal recording sheets is one of such recent approaches. A problem with this dry system is that in order to meet the requirement of the medical industry for producing high-quality images, thermal films must have high sensitivity but such films are also sensitive to humidity changes.
If the sheets of such humidity-dependent thermal film of high sensitivity are handled in the usual manner or if they are contained in the usual magazine, the thermal films will absorb or release moisture with the lapse of time, whereby the film sensitivity changes, making it difficult to record images of high quality in a consistent manner. Take, for example, the case where the thermal film is cut into sheets, which are transferred into the magazine. Also suppose that some of the sheets are processed whereas the remainder is left in the magazine for a relatively long time, e.g., a week. During the storage period, a sensitivity variation will take place due to humidity changes. If the remaining films are processed to reproduce the original image after one week, they will have a considerably different image density than the initially processed films even if the original image is the same.
Therefore, in order to avoid this problem, thermal films have to be handled under such conditions that the humidity is kept as constant as possible, for example, vapor tightness or airtightness is insured to provide effective moisture control.